Car bombs killed at least 21 people in three Iraqi cities Monday, as the leaders of the country's major political blocs met for the first time since parliamentary elections in March.

A blast in the southern Shi'ite city of Basra left at least five people dead and 30 wounded. Earlier, two separate attacks targeted buses carrying Iranian pilgrims in the southern Shi'ite holy cities of Najaf and Karbala, killing at least 16 people and wounding 50 more.

Hundreds of thousands of pilgrims visit Iraq's holy Shi'ite shrines every year. There was no claim of responsibility for Monday's attacks, but Sunni militant groups - who view Shi'ite Muslims as apostates - often target the pilgrims.

The attacks came as Iraqi politicians, including Prime Minister Nouri al-Maliki and his main rival, former prime minister Ayad Allawi, gathered in the northern Kurdish city of Irbil in an inconclusive effort to resolve Iraq's long political deadlock.

Mr. Maliki called for an increased effort to rebuild Iraq's infrastructure, while Mr. Allawi talked about the need for real partners in political decision-making. The session ended without any agreement.

The talks are scheduled to continue Tuesday in Baghdad. Representatives of several factions attended, including followers of anti-U.S. cleric Muqtada al-Sadr, who supports Mr. Maliki. Mr. Allawi's Sunni-backed Iraqiya alliance edged out Mr. Maliki's State of Law bloc in parliamentary elections in March, but so far both parties have failed in their attempts to form a government.

The country has been in a political deadlock since inconclusive parliamentary elections in March. Some politicians have been quoted as saying the two sides are close to a power-sharing deal. Others have denied a deal is close.

U.S. Secretary of State Clinton refused to answer questions Monday about whether a deal was in place. But she told reporters during a visit to Melbourne, Australia, the time has come for Iraq to finally form what she called an inclusive government. Iraq's Supreme Court last month ordered the parliament to resume its sessions and elect a new leader.

Several Iraqi human rights groups have filed a lawsuit in an effort to force members of Iraq's parliament to return at least $40 million received in salaries since elected in March. The group says it will launch a legal battle against the 325 lawmakers who have convened only once since the March 7 polls - for a 20-minute swearing-in session.